1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to a sheet feeding apparatus and an image forming apparatus including a plurality of sheet containing devices mounted one above another with an overlap in a vertical direction.
2. Related Background Art
Up to now, in an image forming apparatus provided with a sheet feeding apparatus including a sheet containing device such as a sheet feeding cassette, sheets are stacked on a plurality of sheet feeding cassettes which are detachably mounted to an apparatus main body one above another with an overlap in a vertical direction, and are sequentially fed to an image forming portion, and then an image is formed on a sheet at the image forming portion.
In such the image forming apparatus, as disclosed in Japanese Patent Application Laid-open No. H07-61613, sheets with different sizes are contained correspondingly in the plurality of sheet feeding cassettes mounted one above another with an overlap in a vertical direction, and the sheets are selectively fed to an image forming portion from the plurality of sheet feeding cassettes according to a designated size of the sheet.
FIG. 6 shows a structure of a conventional image forming apparatus including a plurality of (two) sheet feeding cassettes overlapping with each other in the vertical direction. An upper and lower sheet feeding cassettes 105 and 109 are detachably contained in a width direction with respect to the apparatus main body 100 by a cassette drawer device 108 and 112 for slidably holding the sheet feeding cassettes 105 and 109 in a direction orthogonal to a sheet feeding direction (hereinafter referred to as “width direction”).
Sheets S contained in the sheet feeding cassettes 105 and 109 are fed out by sheet feeding rollers 106 and 110 which are driven by a driving transmission apparatus to be rotated, and then are separated one by one by separating units 107 and 111. After that, the separated sheets are conveyed to an image forming unit 104. It should be noted that in FIG. 6, a partition plate 113 partitions the upper sheet feeding cassette 105 and the lower sheet feeding cassette 109. The lower sheet feeding roller 110 is positioned below the partition plate 113, that is, below a bottom of the upper sheet feeding cassette 105.
It should be noted that the cassette drawer devices 108 and 112, which detachably accommodate the sheet feeding cassettes 105 and 109 arranged in the vertical direction, has a structure as shown in FIGS. 7A, 7B, and 7C. FIG. 7A is a front view showing the cassette drawer device 108, 112 viewed from a direction toward which the cassette is drawn out therefrom. FIGS. 7B and 7C are perspective views showing a state in which the sheet feeding cassette 105, 109 is mounted in the cassette drawer device 108, 112 and a state in which the sheet feeding cassettes 105, 109 are drawn out from the-cassette drawer device 108, 112, respectively.
As shown in FIGS. 7A to 7C, the cassette drawer device 108 (108L and 108R), 112 (112L and 112R) is arranged outside the sheet feeding cassette 105, 109, and includes a base member 108a, 112a that is fixed on a front-and-rear side plate 100a, 100b of the apparatus main body 100 (refer to FIG. 6) and a slide member 108b, 112b that is slidably held in the base member 108a, 112a. 
The sheet feeding cassette 105, 109 is mounted to the slide member 108b, 112b, thereby being detachably mounted into the apparatus main body 100 through the intermediation of the cassette drawer device 108, 112.
However, in such the conventional sheet feeding apparatus and the image forming apparatus, when the plurality of sheet feeding cassettes are provided one above another with an overlap in a vertical direction, a height of the apparatus main body increases. When the height of the apparatus main body thus increases, for example, in a case of a multifunction printer provided with a scanner or the like on a top surface of the apparatus main body, there is a problem in that a position of an original table for stacking an original is higher, and operability thereof deteriorates.
On the other hand, in the conventional image forming apparatus, a sheet feeding unit provided with sheet feeding rollers 106 and 110 is fixed to a feed frame (not shown) provided to the apparatus main body 100. In this case, it is widely recognized that rigidity of the sheet feeding unit has much to do with a sheet feeding performance and image quality.
For example, in a sheet feeding and separating operation, when the sheet feeding unit receives a reaction force from the separating units 107 and 111 through the sheet feeding rollers 106 and 110 and is deformed by the reaction force, a failure in sheet feeding or skew feeding of sheets is caused. As a result, deterioration in image quality or the like is caused.